JP2006139905A - System and method for tape drive control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for attenuating movement of a head of a tape drive. <P>SOLUTION: This method includes a step in which a position of the head is measured by a position sensor over a hour, a step in which movement of the head is attenuated based on the position of the head measured over a hour, and a step in which attenuation is adjusted by varying parameters of the position sensor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tape drive. Specifically, the present invention relates to measuring the position of a read / write head of a tape drive.

  It is well known to record at high density on multiple tracks of a magnetic tape. In one configuration, parallel tracks extend along the length of the magnetic tape. The magnetic tape moves across the read / write head and data is recorded or read. During recording or playback, the tape moves in the vertical direction, so the head must remain in a lateral position fixed with respect to the tape.

  Some existing tape storage systems include a mechanism that allows the read / write head to be positioned at the centerline of the track when the read / write process begins. Once the read / write process begins, there is no correction if a misalignment occurs between the head and the track centerline.

  In order to increase the storage capacity to meet the increasing demand, the track density, which is the number of tracks per distance (eg, inches), must be increased. As the track density increases, the track pitch and width decreases. For proper read / write operations, the magnetic head must remain at or very close to the track centerline, increasing the need for accuracy due to the higher track density.

  A conventional tape drive system is shown in FIG. This system includes a tape drive 12 connected to a host computer 10 by a cable 16 and an attached tape cartridge 14. The tape drive 12 includes a receiving slot 22 into which the tape cartridge 14 is inserted. The tape cartridge 14 includes a housing 18 that contains a length of magnetic tape 20. The tape drive 12 is preferably compatible with the associated host computer and can take on any of a variety of cartridge or cassette linear formats.

  A general configuration of the tape drive 12 is shown in FIG. The tape drive 12 of FIG. 2 includes a deck 24 that includes moving parts and a control card 26 that includes various circuits and buses. The deck 24 rotates the head assembly 28 that contacts the tape 20 of the tape cartridge inserted into the tape drive 12, the supply reel 30, and the take-up reel 32 to read and write data and read the servo pattern, respectively. Motors 34 and 36 for the purpose. For the dual reel type tape cartridge 14, both reels 30, 32 are included in the tape cartridge 14. However, for the single reel type tape cartridge 14, only the supply reel 30 is included in the tape cartridge 14, and the take-up reel 32 is provided in the tape drive 12. Although not shown in FIG. 2, the deck 24 further removes a mechanism for moving the head assembly 28 across the width of the tape 20, a mechanism for holding the inserted tape cartridge, and removing the inserted tape cartridge. And a mechanism for.

  The control card 26 includes a microprocessor (MPU) 38, a memory 42, a servo control unit 44, a data flow unit 46 and an interface all connected to the MPU 38 through an internal bus 40 for overall control of the tape drive 12. The control unit 48 includes a motor control unit 50 and a head control unit 52 both connected to the servo control unit 44 and a data channel unit 54 connected to the data flow unit 46. Although the memory 42 is shown in FIG. 2 as a single hardware component, it is actually comprised of a read only memory (ROM) that stores a program to be executed by the MPU 38 and a working random access memory. Is preferred. The servo control unit 44 manages speed control for the motors 34 and 36 and position control for the head assembly 28 by transmitting respective control signals to the motor control unit 50 and the head control unit 52. Motor control unit 50 and head control unit 52 respond to these control signals by physically driving motors 34 and 36, respectively, and positioning head assembly 28.

  The head assembly 28 includes a servo head that reads data from servo tracks or servo bands on the tape 20. The control card 26 utilizes data from the servo track to generate a position error signal (PES) that is used by the servo control unit 44 so that the head control unit 52 positions the head assembly 28. In some conventional designs, the head assembly 28 includes a voice coil motor (VCM) 56 that receives electrical signals from the head control unit 52 and positions the head assembly 28 according to the received signals. .

  The data flow unit 46 compresses data to be written on the tape 20, decompresses data read from the tape 20, corrects errors, and is connected not only to the data channel unit 54 but also to the interface control unit 48. Yes. The interface control unit 48 is provided for transmitting data to and from the host computer via the cable 16. The data channel unit 54 is essentially a circuit that modulates and demodulates data. That is, when data is written to tape 20, it performs digital / analog conversion and modulation of the data received from data flow unit 46, and when data is read from tape 20, it is read by head assembly 28. Performs analog / digital conversion and demodulation of the data.

  In one type of tape drive, the head control unit 52 and head assembly can be considered essentially a secondary type spring mass actuator system. This type of actuator system can have a fundamental resonance that is usually in the loop bandwidth. One of the common characteristics of secondary spring mass actuator systems is that the damping is insufficient unless the damping is designed as part of a mechanical assembly. Damping provides the actuator with a controlled step response. Excessive attenuation will cause the system to malfunction, but lack of attenuation will cause the system to ring at the fundamental frequency.

  In some applications, damping is achieved by mechanical means such as the use of grease or ferrofluid. One system of this type is taught in US Pat. No. 5,739,984. In another application, the PES signal or back EMF signal is used to estimate the velocity state variable for the head assembly 28 that is to be attenuated and this information is fed back to the servo control unit 44. US Pat. No. 6,359,748 teaches such use of a back EMF signal. However, these two methods have certain drawbacks. For example, PES is continuous only in a defined zone, which has relative position information between the head and heap, making the estimation process rather difficult and limited to PES availability. In some situations, the servo head is very close to the edge of the servo band. Impact and vibration disturbances and large lateral tape movements due to swaying wound tape layers cause the servo head to move out of the servo band, thereby causing loss of PES. Back EMF signals are difficult to use because their values usually depend on actuator electrical and physical parameters, inductance, coil resistance, sensing resistance, and magnetic properties, and the actuator speed is estimated as a function of back EMF. Make the task very difficult and potentially inaccurate.

  For systems that have a predetermined tape portion where the feedback signal is located, such as the linear tape open (LTO) servo feedback method, a discontinuous form of the feedback signal can provide a problem. The discontinuous feedback signal is generated for the following reasons, for example. That is, the head may move away from the servo band when the tape suddenly goes up or down. While the head is tracking very close to the edge of the servo band, external shocks or vibrations can push the head out of the servo band.

The use of a VCM with little or no damping in an environment that exhibits discontinuous feedback can cause the head to vibrate at its natural frequency. Due to the vibration of the head, it usually takes time to restore tracking, which results in a decrease in system performance.
US Pat. No. 5,739,984 US Pat. No. 6,359,748

  Accordingly, it is an object of the present invention to provide a system and method for reducing head vibration. Another object of the present invention is to reduce head vibration by providing an adjustable damping system that includes an optical sensor for sensing the position of the head.

  The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the following detailed description, the principles and practice of the invention. It is useful to explain.

  Embodiments of the present invention are described herein in the context of systems and methods for tape drive control. Those skilled in the art will appreciate that the following detailed description of the present invention is illustrative only and is not intended to be limiting in any way. Those skilled in the art will readily suggest that other embodiments of the invention themselves have the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to represent the same or similar parts.

  For clarity, all common features and implementations described herein are not shown or described. Of course, when developing any of these actual executions, many executions must make specific decisions in order to achieve specific goals for the developer, such as following application and business constraints. It will be understood that these specific goals will vary from run to run and from developer to developer. Furthermore, such development efforts may be complex and time consuming, but would not be a routine engineering project for those skilled in the art who would benefit from this disclosure.

  In accordance with the present invention, components, method steps, and / or data structures can be performed using various types of operating systems, computing platforms, computer programs, and / or general purpose machines. In addition, less versatile devices such as hard-wired devices, field programmable gate array (FPGAs) application specific integrated circuits (ASICs) are also within the scope and spirit of the inventive concepts disclosed herein. Those skilled in the art will appreciate that they may be used without departing.

  Turning now to FIGS. 3-6A, an optical position sensor 59 including a light emitter assembly 60 is shown, which includes a light emitting diode LED 62 and a light sensor assembly 64. The emitter assembly 60 and the optical sensor assembly 64 are attached to the housing body 66 and the housing cap 68. Optical position sensor 59 is assembled with read / write head assembly 72 and VCM 102. An adjustable screw 74 is threadably engaged by a central spring clamp 78. FIG. 6 shows an adjustable screw 74 placed near the LED 62 such that the head of the screw 74 partially blocks light from the LED 62 to the light sensor assembly 64. The adjustable screw can be rotated and moved up and down to a selected position as indicated by arrow 76 for calibration purposes.

  As shown very well in FIG. 6A, the VCM 102 includes a voice coil assembly 80 that is substantially cylindrical, the voice coil assembly 80 having a cylindrical shape formed in a voice coil housing 82. Located in the lumen. Top spring element 84 is connected by a central spring clamp 78 to the top of voice coil assembly 80 and voice coil housing 82, and top spring element 84 provides a flexible connection between assembly 80 and housing 84. To do. Although not shown, a similar bottom spring element is connected to the bottom of the voice coil assembly 80 and the voice coil housing 82. These top and bottom spring elements provide a flexible connection and allow limited vertical movement of the voice coil assembly 80 relative to the voice coil housing 82. Read / write head assembly 72 is rigidly connected to central spring clamp 78.

  Next, read / write head 72, voice coil assembly 80, central spring clamp 78, and adjustable screw 74 are all understood to be rigidly connected to one another so that they all move up and down together as a unit. I want to be. On the one hand, the optical position sensor 59 is isolated from these components so that it does not move with the above components. Rather, the optical position sensor 59 is rigidly connected to the voice coil housing 82, and the voice coil housing 82 is rigidly connected to the tape drive housing. Thus, as the read / write head assembly 72 moves up and down as indicated by arrow 86, the head of the adjustable screw 74 partially blocks the light received by the light sensor assembly 64 from the LED 62, and the degree of this light blocking is , Directly proportional to the relative vertical position of the optical position sensor 59 relative to the read / write head assembly 72. The optical sensor assembly 64 generates an electrical signal corresponding to the light it receives, which is used by the control system described below.

  Turning now to FIG. 7, a block diagram that schematically illustrates a control system 98 in accordance with a preferred embodiment of the present invention is shown. The control system includes a summer 101, an amplifier 100, and a VCM 102 attached to the head assembly 28. The gain of the amplifier 100 is Ka, and the transfer function between the VCM and the head assembly is Gp. The control system 98 further includes a feedback loop 104 that includes an optical sensor 60 and a filter 106, and block 108 indicates that the gain C of the feedback loop can be controlled. Filter 106 is AC coupled and has the following transfer function: Ie

  The variable k is a gain and τ is a time constant. The filter 106 can be a lead lag filter that differentiates the input signal and adds low-pass filtering.

  The control system 98 is connected such that the summer 101 receives the signal from the tracking loop and subtracts the signal from the feedback loop 104 from the tracking loop signal. A signal from the tracking loop represents a target position of the VCM and is generated by the servo control unit 44 and the head control unit 54. However, the signal from the tracking loop can be generated by conventional means.

  In practice, the variability in the gain of the optical sensor 60 due to aging, temperature, humidity, and many lot variations may result in system variability. Furthermore, while excessive attenuation results in a slow and slow functioning system, insufficient attenuation can result in excessive overshoot during transients. Therefore, it is desirable to have the ability to control the degree of attenuation to account for specific characteristics of the system. In other words, the attenuation is adjustable.

  Furthermore, the ability to control attenuation is desirable to obtain a system's assertable response in both loop gain and phase. For example, for the system modeled here, it has been found that higher attenuation results in a larger phase in the critical region desirable for phase margin and stability. However, lower attenuation results in greater suppression in the critical region. Therefore, there is an optimal attenuation value that will satisfy both the phase and suppression requirements. This provides a calibration algorithm that adjusts to accommodate the attenuation and maintains the optimum value.

  It has been found that controllable attenuation can be achieved by calibrating the feedback loop 104 using an LED circuit. This is true because the LED current is proportional to the attenuation applied by the feedback loop 104.

  To calibrate the feedback loop 104, the calibration system 120 shown in FIG. 8 is used. Calibration system 120 includes an attenuation adjustment algorithm 122 that can be executed in a microprocessor, such as microprocessor 38. The system also includes two digital / analog converters (DACs) 124, 126 for receiving the digital signal calculated by the attenuation adjustment algorithm 122. The first DAC 124 transmits the analog signal to the summer 101 and the second DAC 126 establishes a setting for the LED current to the photosensor 60.

  In operation, the attenuated VCM position signal controls the position of the head assembly 28. As represented by summer 130, the lateral movement of the tape is added to the lateral movement of the head assembly, and the resulting total movement is measured by conventional servo control system 44 to generate PES 132.

  The attenuation adjustment algorithm 122 sends a set of digitized sinusoidal signals to the VCM amplifier reference DAC 124 that controls the line labeled “From Tracking Loop” in FIG. The attenuation adjustment algorithm 122 modifies the PES data as the tape moves across the head at a constant speed. The attenuation adjustment algorithm 122 performs this as a background task when the tape is moving and the drive is not performing read / write data transfers but is rewinding or searching for a position. Therefore, normal operation of the drive is not interrupted. This background calibration continuously maintains optimum attenuation.

  The attenuation adjustment algorithm 122 calculates the transfer function of the PES for the sensor current LED using a curve fitting algorithm and sets it using quadratic function fitting. This is done for three different LED currents: high, medium and low current. Once the attenuation adjustment algorithm 122 finishes calculating the attenuation coefficient for all three different LED currents, the algorithm 122 fits a cubic function to calculate the LED current for the target attenuation coefficient. The algorithm 122 can then load this value into the LED current control DAC 126.

  Although the embodiments and application examples of the present invention have been illustrated and described, it is possible to make many changes from the above without departing from the concept of the present invention in this specification. It will be clear to the contractor.

It is a figure which shows the conventional tape drive system. FIG. 6 is a block diagram illustrating an exemplary arrangement of a control card and tape drive according to the prior art. FIG. 3 is an isometric exploded view of a portion of an optical position sensor according to a preferred embodiment of the present invention. It is a figure which shows the assembled state of the component shown in FIG. FIG. 4 shows an optical position sensor according to a preferred embodiment of the present invention when connected to a read / write head and a VCM. FIG. 3 is a cross-sectional view of an optical position sensor, a read / write head, and a VCM. FIG. 2 is a partially exploded isometric view of an optical position sensor, read / write head, and VCM. 1 is a block diagram of a control system according to a preferred embodiment of the present invention. FIG. 3 is another block diagram of a control system according to a preferred embodiment of the present invention.

Explanation of symbols

10 host computer 12 tape drive 14 tape cartridge 16 cable 18 housing 20 magnetic tape 22 receiving slot 24 deck 26 control card 28 head assembly 30 supply reel 32 take-up reel 34 motor 36 motor 38 microprocessor (MPU)
40 Internal bus 42 Memory 44 Servo control unit 46 Data flow unit 48 Interface control unit 50 Motor control unit 52 Head control unit 54 Data channel unit 56 Voice coil motor (VCM)
59 Optical position sensor 60 Light emitter assembly 62 Light emitting diode LED
64 Optical Sensor Assembly 66 Housing Body 68 Housing Cap 72 Read / Write Head Assembly 74 Adjustable Screw 76 Arrow 78 Center Spring Clamp 80 Voice Coil Assembly 82 Voice Coil Housing 84 Top Spring Element 86 Arrow 98 Control System 100 Amplifier 101 Summarizer 102 Voice Coil motor (VCM)
104 Feedback Loop 106 Filter 120 Calibration System 122 Attenuation Adjustment Algorithm 124 First Digital / Analog Converter (DAC)
126 Second digital / analog converter (DAC)
130 Totalizer 132 Position Error Signal (PES)

Claims (8)

A sensor for measuring the position of the head of a tape drive,
A light emitter movably coupled to the head;
A photosensor movably coupled to the head and rigidly coupled to the light emitter and disposed to receive light from the light emitter;
And a light breaker arranged to block the light beam and firmly connected to the head.   The sensor according to claim 1, wherein the light emitter is movably connected to the head by a spring.   The sensor according to claim 1, wherein the optical sensor is movably connected to the head by a spring.   The sensor of claim 1, wherein the light breaker has a breaker head disposed at least partially within the light beam.   The sensor of claim 1, wherein the light breaker is adjustably arranged, arranged and assembled to block a controllable portion of the light beam. A sensor for measuring the position of the head of a tape drive,
A housing movably coupled to the head;
A light emitter rigidly connected to the housing;
A photosensor disposed to receive light from the light emitter and rigidly coupled to the housing;
And a light blocker firmly connected to the head so as to block at least a part of the light beam.   The sensor according to claim 6, wherein the housing is movably connected to the head by a spring. The sensor according to claim 6, wherein the sensor measures the position of the head as compared with the housing.

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